1. Field of the Invention
The present invention relates generally to hydraulic dampers for vehicular suspension. In particular, the present invention is concerned with an internal fluid accumulator and method to absorb and dissipate energy when a fluid pressure spike occurs inside a hydraulic damper.
2. Description of the Related Art
Hydraulic dampers (shock absorbers and struts) include a reciprocable piston and piston rod slidably mounted in a fluid-filled cylinder. The piston divides the interior of the cylinder into upper and lower chambers. A valve assembly in the piston provides a restricted fluid path between the chambers. A reservoir tube concentrically mounts and cooperates with the cylinder to form a fluid reservoir. The lower end of the cylinder is closed by a compression or base valve assembly. During a compression stroke, fluid travels from the lower chamber through the piston valve assembly to the upper chamber. The fluid equivalent of the rod volume is discharged through the base valve assembly to the reservoir. During a rebound stroke, fluid travels from the upper chamber through the piston valve assembly to the lower chamber. Also, fluid travels from the reservoir through the base valve assembly to the lower chamber to compensate for the rod volume. The restriction of fluid through the piston and base valve assemblies provides the level of damping in a damper.
The use of a bypass channel between the upper chamber and the reservoir is well-known in dampers. Many such dampers incorporate a quick-acting electric solenoid valve assembly to open and close the bypass channel. When the solenoid valve assembly is opened, fluid travels from the upper chamber to the reservoir through the bypass channel. This redirection of fluid changes the damping characteristic of the damper to a "soft" setting, since the bypass channel permits fluid flow with less restriction than the piston and base valve assemblies. When the solenoid valve assembly is closed, fluid is forced to flow through the piston and base valve assemblies in the usual manner, resulting in a "firm" setting.
As a damper reciprocates, fluid is forced through various passages. When this flowing fluid is quickly decelerated by closing the solenoid valve assembly, the change in fluid momentum causes a pressure spike or rise in the fluid upstream of the solenoid valve assembly. The pressure spike causes the piston to accelerate at high gravitational levels, thereby exciting body elements to which the piston rod is mounted and producing structural vibration and airborne noise over a wide band of audio frequencies.
The art continues to seek improvements. It is desirable to minimize the vibration and noise in body elements which can result from the closing of a solenoid valve assembly in a hydraulic damper.